This application is based on and incorporates herein by reference Japanese Patent Application No. 2000-396730 filed on Dec. 27, 2000 and Japanese Patent Application No. 2001-189561 filed on Jun. 22, 2001.
1. Field of the Invention
The present invention relates to a core of a motor, which has a plurality of core sheets stacked together. The present invention also relates to a method for stacking the core sheets.
2. Description of Related Art
Generally, a motor has a rotatable shaft, to which a core and a commutator are secured. Windings are wound around the core and are electrically connected to the commutator. The core is formed by stacking a plurality of core sheets together.
With reference to FIG. 11, for example, a casing 52 of one previously proposed motor 51 receives a core 53. The core 53 includes a plurality of stacked core sheets 61. Each core sheet 61 has an inner annular portion 62 and an outer annular portion 63. A rotatable shaft 57 is received through the inner annular portion 62 of each core sheet 61. The outer annular portion 63 of each core sheet 61 has a plurality of teeth 64 that extend radially outward from the outer annular portion 63. Window openings 65 are arranged in a space between the inner annular portion 62 and the outer annular portion 63 of each core sheet 61. The inner annular portion 62 is connected to the outer annular portion 63 through a plurality of stays 66. A commutator 54 is secured around a lower end portion of the rotatable shaft 57, which is located on a first surface 53a side of the core 53. Brushes 55 are arranged to slide along the commutator 54. A bearing 56 is secured to an upper end portion of the rotatable shaft 57, which is located on a second surface 53b side of the core 53. Non-contact type seals 73 are arranged in the bearing 56.
In this type of the motor, brush powder, which is generated from the brushes 55 through abrasion when the brushes 55 slide along the commutator 54, can penetrate into the bearing 56. To address this problem, one such motor has a dustproof cover 71 secured to the bearing 56 to cover the bearing 56, as shown in FIG. 12A. In place of the non-contact type seals 73, another such motor has contact type seals 72, which prevent the penetration of the brush powder into the bearing 56, as shown in FIG. 12B.
However, the dustproof cover 71 shown in FIG. 12A is a separate component that is provided separately from the bearing 56. This causes an increase in the number of the required components of the motor 51. Furthermore, a separate step is required to install the dust proof cover 71 in the bearing 56. Use of the contact type seals 72 shown in FIG. 12B causes an increase in a manufacturing cost of the motor in comparison to the other motor that uses the non-contact type seals 73. As a result, there is a disadvantage of increasing the manufacturing cost of the motor 51.
The present invention addresses the above disadvantage. Thus, it is an objective of the present invention to provide a core of a motor, which includes a plurality of core sheets stacked together and allows a reduction in a manufacturing cost of the motor. It is another objective of the present invention to provide a method for stacking the core sheets of the core.
To achieve the objectives of the present invention, there is provided a core of a motor including a plurality of core sheets, which are of one type and are stacked together. Each core sheet includes an inner annular portion, an outer annular portion and a plurality of stays. The stays are arranged at equal angular intervals in a circumferential direction of the core sheet and connect the inner annular portion to the outer annular portion, so that each adjacent two stays of the core sheet define a window opening therebetween. The inner annular portion has a rotatable shaft securing hole that extends through a center of the inner annular portion in an axial direction of the core to receive a rotatable shaft of the motor. The outer annular portion includes a plurality of teeth that are arranged at equal angular intervals in the circumferential direction of the core sheet and extend radially outward from the outer annular portion. Each adjacent two teeth of the core sheet define a slot therebetween. Each core sheet further includes at least one projection, at least one recess and a receiving portion, which are all arranged along a concentric circle that is concentric to a rotational axis of the rotatable shaft of the motor. The at least one projection is arranged in a first axial end surface of the core sheet. The at least one recess and the receiving portion are arranged in a second axial end surface of the core sheet in such a manner that each one of the at least one projection of the core sheet is opposed to a corresponding one of the at least one recess of the core sheet in the axial direction of the core. At least two adjacent core sheets of the core sheets are displaced one after the other by a predetermined displacement angle in a circumferential direction of the core in such a manner that the stays of one of the at least two adjacent core sheets are partially overlapped with the stays of the other one of the at least two adjacent core sheets, respectively, and the slots of the one of the at least two adjacent core sheets are aligned with the slots of the other one of the at least two adjacent core sheets in the axial direction of the core, respectively. The second axial end surface of the one of the at least two adjacent core sheets is opposed to the first axial end surface of the other one of the at least two adjacent core sheets. Each one of the at least one projection arranged in the first axial end surface of the other one of the at least two adjacent core sheets is substantially, entirely received in a corresponding one of the receiving portion and the at least one recess arranged in the second axial end surface of the one of the at least two adjacent core sheets. Thus, the first axial end surface of the other one of the at least two adjacent core sheets closely contacts the second axial end surface of the one of the at least two adjacent core sheets.
The at least one projection, the at least one recess and the receiving portion of each core sheet can be arranged such that each core sheet is engageable with adjacent one of the core sheets only when each core sheet is placed in one of first and second angular positions with respect to the adjacent one of the core sheets. Each core sheet is placed in the first angular position when the receiving portion of each core sheet is aligned with the receiving portion of the adjacent one of the core sheets in the axial direction of the core. Each core sheet is placed in the second angular position when each core sheet is displaced by the predetermined displacement angle with respect to the adjacent one of the core sheets in the circumferential direction of the core.
Also, the core sheets can be progressively displaced one after the other by the predetermined displacement angle in the circumferential direction of the core in such a manner that the stays of the core sheets form a plurality of stairstep-shaped guide walls that are circumferentially spaced from each other and spirally extend in the axial direction of the core. The stairstep-shaped guide walls guide and force air to flow in the axial direction of the core through the window openings of the core sheets when the core is rotated.
Furthermore, to achieve the objectives of the present invention, there is also provided a method for stacking the core sheets of the core of the motor. The method includes a process of stacking the core sheets such that the core sheets are progressively displaced one after the other by a predetermined displacement angle in a circumferential direction of the core in such a manner that the stays of the core sheets form a plurality of stairstep-shaped guide walls that are circumferentially spaced from each other and spirally extend in the axial direction of the core, while the slots of one of each two adjacent core sheets are aligned with the corresponding slots of the other one of the two adjacent core sheets in the axial direction of the core, and the stairstep-shaped guide walls guide and force air to flow in the axial direction of the core through the window openings of the core sheets when the core is rotated.